Swapping Div-tags With 2 Buttons

I´m completely new at javascript, and I got a little issue. I want to be able to have some text in my index-page and 2 buttons to change this text back and forth with diffrent text. Say i have one headline like this

<div id="first">
<h1>Hello world</h1>
<p>Lorem ipsum etc............</p>
</div>

and i want 2 buttons under this text beeing able to swap all this code for say this:

<div id="second">
<h1>Hello president</h1>
<p>Lorem ipsum etc............</p>
</div>

and most likely sevral more swaps, so the buttons would work like a library function.